1. Field of the Invention
This invention relates generally to a composite structural panel, and more particularly to an asymmetrical concrete backerboard having fiberglass mesh reinforcement on one side, and an impervious reinforcement membrane on the opposite side of the board.
2. Description of Related Art
The conventional backerboard is made up of a rectangular panel of solid concrete, the concrete core, having both major surfaces covered with fiberglass. The fiberglass adds strength to the board, and provides only limited resistance to water penetration through the board. Concrete backerboards are used extensively in the construction of interior and exterior floors, walls and ceilings. The concrete backerboard is a superior substrate or underlayment for stucco, ceramic tile, marble, and other tile-like surfaces located in wet areas, such as shower walls and bathtub surrounds, and building exterior walls.
Typically, the concrete core of the backerboard is a low density, high compressive strength, concrete core. The fiberglass mesh reinforcement layers overlay both major faces of the core, with each of these pervious fiberglass layers themselves covered with a thin layer of Portland cement. Backerboards have textured cementitious surfaces that provide for a high strength bond with mastics and Portland cement mortars that are used to adhere tile to the substrate in wet areas.
While the conventional backerboard is generally stable and water resistant, it is not an ideal construction panel for use in wet environments due to several inherent limitations. For example, it is generally recommended by backerboard manufactures, and required by most building codes, to use an additional impervious moisture barrier behind the backerboard. Thus, contractors are forced to install the backerboard and separate moisture barrier in the field, at the construction site. Use of an impervious barrier membrane with the backerboard provides protection for the wood or steel structures under or behind the backerboard, and contains the moisture in the wet area. Examples of commonly used moisture barriers are felt paper, Tyvek®, spunbonded olefin and polyethylene.
An exemplary patent in this field includes U.S. Pat. No. 3,284,980 to Dinkel disclosing a precast panel of cement and aggregate reinforced with a skin membrane of fibrous material. Backerboard manufacturing techniques include a lightweight aggregate core faced on each side or face with a fiberglass mesh material bathed in a slurry of neat cement and pressed against the aggregate core, such that when the neat cement and the aggregate core are cured, there is provided a composite, fiberglass mesh reinforced, cementitious panel. U.S. Reissue Pat. No. Re 32,037 to Clear is a method for manufacturing cementitious reinforced panels and illustrates a concrete panel 11 having reinforcement layers 12, 13 and a polyethylene layer 20 adjacent one of the layers 12, 13. Layers 12 and 13 are described as mesh reinforcing elements, preferably constituting fiber mesh like pervious webs, each entrained in hydraulic cement. Layer 20 is a carrier sheet placed under reinforcing element 12 during manufacture. Yet, such methods of constructing backerboards are not only deficient because they produce an inferior wet-area panel, but also because they require the use of a carrier sheet.
It is evident from the prior art that an improved backerboard and method of constructing such an improved backerboard is needed. It can be seen that there is a need for a backerboard having at least one waterproof surface that can be delivered ready-made to the construction site, and a method for producing such a backerboard without resort to a carrier sheet.